Previously, the recesses for accommodating the line foreseen between the projections were constructed withsuch a height that air could be circulated over or under the line. This required on the one hand holding devices of special construction for the line, and on the other hand the height of the tempering system between the inner layer and the outer layer usually had to be twice as long as the diameter of the line.
In addition, it was previously assumed that the essential task of a thermal conductive sheet is to transport the heat or the cold from the line to the surface of the construction, and to immediately distribute it over a larger surface. In the scope of the present invention it was established that in the performance of this task only a modest portion of the heat can be transported, namely by conduction, so that the temperature difference between the line and the surface of the closure is to be sure reduced, but that it is still too high. This leads to heat accumulation, and hence to the necessity of operating with, e.g. in the case of warm-water floor heating, a higher supply temperature. This circumstance reduces the economy of the heating system to a state which is lower than if the supply temperature could be lowered further.